This invention relates to a variable capacity vane compressor which is adapted to vary the compression starting timing for varying the capacity thereof, and more particularly to a vane compressor of this kind which is free from chattering of the vanes and at the same time excessive wear in the tips of the vanes.
In order to prevent chattering of vanes due to insufficient vane back pressure acting thereon and at the same time avoid wear in the tips of the vanes due to excessive vane back pressure, a variable capacity vane compressor has conventionally been proposed e.g. by Japanese Provisional Utility Model Publication (kokai) No. 1-141391 assigned to the applicant of the present application, which has a central annular groove formed in one end face of one side block facing a rotor and communicatable with each of vane back pressure chambers formed in the rotor to introduce pressure created from discharge pressure Pd therethrough into the each vane back pressure chamber while the associated vane is moving from a suction stroke-starting position to an intermediate position during the compression stroke. Oil supply holes are formed in the same side block and communicatable with each vane back pressure chamber to introduce oil under pressure created from discharge pressure Pd, which is higher than the pressure from the annular groove, into the each vane back pressure chamber for preventing a decrease in the vane back pressure Pk after the vane back pressure chamber is brought out of communication with the annular groove and until the delivery stroke is completed.
According to the proposed compressor, the oil is introduced from the oil supply holes into the vane back pressure chamber under the same pressure irrespective of whether the compressor is in partial capacity operation or in full capacity operation, after the vane back pressure chamber are brought out of communication with the annular groove and before completion of the discharge stroke.
However, in a vane compressor like the proposed compressor, as shown in FIG. 8, when the compressor is brought into partial capacity operation wherein the discharge pressure Pd is low so that the capacity assumes the minimum value, the vane back pressure Pk largely drops, resulting in chattering of the vanes. The reason for the large drop in the vane back pressure Pk is as follows: Another side block which is located on the opposite side of the rotor to the one side block is always acted upon by suction pressure Ps at an end face thereof remote from the rotor. Therefore, when the compressor is in partial capacity operation where the discharge pressure Pd is low, the rotor is urged by the other side block and biased toward the one side block. Accordingly, the clearance between the one side block and the rotor becomes smaller so that the oil is introduced in reduced amounts from the oil supply holes into the vane back pressure chambers, resulting in a large drop in the vane back pressure Pk.
One way to prevent such a large drop in the vane back pressure Pk would be to enlarge the opening area of the oil supply holes so as to increase the amount of oil to be supplied therethrough. However, according to this method, once the rotor is biased toward the one side block, the actual amount of oil cannot increase to a desired degree even with the enlarged oil supply holes. Further, if the opening area of the oil supply holes is enlarged, when the rotor is biased toward the other side block, the vane back pressure Pk will become excessively high, resulting in wear in the tips of the vanes as well as increased power required for driving the compressor.